The present invention generally relates to the testing of IC devices such as packaged semiconductor chips (also referred to as packaged dies), and more particularly relates to devices for maintaining the temperature of an integrated circuit (IC) device under test (DUT) in various packages.
Thermal control units have been devised to test packaged IC chips under conditions in which the DUT's temperature is raised, maintained, or lowered during the course of the test. Such units provide thermal contact with the DUT and carry heat away from or add heat to the DUT as required based on a predetermined set point temperature. Such units frequently use a peltier device as a heat pump to achieve such temperature control. Peltier devices are solid-state devices that come in small thin geometries and that can be controlled by a DC current to pump heat away from a contacted device for removal. By reversing the current, the peltier device acts as a heater by pumping heat into a contacted device.
Alternatively, a thermally-conductive electrically-resistive heater can be used to rapidly heat up the DUT, and then rapidly cool down the DUT in combination a (cooling) fluid block, via conduction through the heater.
In thermal control units for IC testing, the ability of the peltier device or the heater to efficiently transfer heat to and away from the DUT is affected by the contact between the peltier device and the other components of the thermal control unit, including the thermal sensor containing pedestal that contacts the DUT. Efficient heat transfer requires large forces pushing the heat transfer surfaces of the peltier device or heater, typically forces that exceed 100 pounds per square inch. The rigid mechanical designs heretofore used in DUT thermal control units to generate these required clamping forces tend to cause the components of the unit to bend or bow in a manner that interferes with thermal contacts made with the peltier device or heater, resulting in degradation of the device's heat transfer capabilities.
Some attempts have been made to overcome these problems. For example, U.S. Pat. No. 7,663,388 Barabi et al. describes a thermal control unit (TCU) for maintaining the set point temperature of an IC device under test (DUT). The TCU has a thermoelectric module (a peltier device), a temperature-control fluid block, a lower pedestal assembly containing a thermal sensor, and an upper cover housing arranged in a stacked relationship along the z-axis of the TCU. A z-axis compliant force is supplied from the TCU's cover housing by means of a spring-type pusher mechanism that supplies a compliant spring force to the stacked arrangement of the fluid block, peltier device, and pedestal assembly. The z-axis compliant force provided by the spring-type pusher mechanism produces efficient thermal contact between the peltier device and the stacked components of the TCU containing the peltier device and allows the peltier device to expand and contract within the TCU to extend the life of the peltier device.
In addition, DUTs may be held in a manner that achieves efficient electrical contact between the I/O contact array of an IC device and the conductor pads of a circuit board. U.S. Pat. No. 7,651,340 to Barabi et al., for example, describes an IC socket cover assembly capable of producing and maintaining precise actuating forces on an IC chip package and capable of efficiently dissipating heat produced by a chip. The assembly includes a pedestal assembly spring-mounted to the bottom of a carrier housing and side leaf springs or other similar force transferring means on the pedestal assembly which transmit a z-axis force to the corner regions of the pedestal assembly for advancing the pedestal assembly in the z-axis direction against an IC chip in the IC socket. The compliance of the leaf springs maintains a constant and precise actuating force on the IC chip when the IC chip is contacted by the pusher end portion or portions of the pedestal assembly. Front, back, and sides of the carrier housing may define a central cavity region above the pedestal assembly for permitting air flow through the carrier housing to improve the heat dissipation capability of the cover assembly.
As described below, the present invention provides improvements to TCUs in the areas of (1) load control and balancing, e.g., to test bare die packages in a manner that ensures application of appropriate compliant forces to different portions of the packages so as to avoid damaging the die, (2) TCU stability during test, and (3) condensation abatement for surfaces of the TCUs susceptible to water or ice accumulation during cold testing.